I posted some photos of a transmission I am working on in another thread: Link to Driven gear removal thread
Rather than continuing drifting that thread I felt I should move the discussion to it's own thread. If all four photos don't show just hit refresh your screen.
I pulled my driven gear off a rusty old stack of drums and when I cleaned them up I found a casting defect and some interesting scoring on the brake drum surface.
The story continues here:
So I went out and tried bands on the scored brake drum. No certain answers but I think I know what happened.
Narrow band position if early ('09-'25) transmission cover is used.
Narrow band position with Late ('26-'27) transmission cover.
Correct wide band with late cover.
Correct set up with lugs pulled in to drum as if the lining has worn out.
From the above I think this wear pattern is probably due to using a narrow band instead of the correct band. An additional possibility is that the correct wide band was used but the lining wore or tore away allowing the lug to dive into the drum damaging the surface.
The scratches are well defined and deep so I believe the edge of a band probably did the damage.
Moral of this story:
Terry, I responded on the other thread before reading this.
Allan from down under.
Terry, now I finally understand why my old wide brake drum looks like this:
Thanks for the investigative reporting!
Eric, there's another one! I am beginning to think that this is not an uncommon thing. I imagine that in the '30's (or anytime since) when cash was tight, if you had a running car which wouldn't stop, you would do what you had to so it would stay in service. That might mean pulling a narrow band off of a rusting hulk for free rather than spend a dime to get a wide band relined.
The brake drum is thicker than the other drums. You can likely chuck it up in a a lathe and pretty it up and polish it with emery. I would not try to make it look like new by turning out the entire grooved surface. You can look at the thickness and make a better decision than I. I would not call it toast.
Ted, in my drum pile I have a few that have been "prettied up" on a lathe. The machinist did a skillful job but the surface is too rough (even so, smooth to the touch) to use as is. If I had a tool post grinder I would try that. My recommendation is to have the drum ground.
I may give polishing the lathe turned drum a try. Maybe try to do a better finish cut... Only if the previous machinist didn't do good enough then how can an untrained home hobbyist hope to do better? For me the decision to use a brake drum requires:
That is pretty much what I think the order of importance is. Fail on any item 1-6 and game over. 7 fail then replace, turn, and ream new bushes.
If anyone wants to see I will photograph a lathe turned drum and post it here.
(Message edited by thorlick on March 20, 2016)
Your determination is likely greater than that of the machinist.
In your picture, the outer edges are higher than in the center. If it were mine and the best drum I could find, I would turn only the outside edges .002" and then sand the rest to remove any sharp edges which could snag and tear the band. I think you would be fine like that and it would not remove the thickness of the drum.
Norman, I got a used drum with a flatter surface. It's not as polished as the old one but I think the bands will take care of that in short order.
That drum looks very good.
Thanks Norm. The strange thing is that there is more space between the low drum and brake drum than the reverse drum.
Is that normal? You can see it in the picture posted above.
Eric, that's normal.
OK, thanks Stephen!